Remove None initializer support (#91)

* `None` legacy initializer support removed
* Default value for `Null` removed

3 files changed, 19 insertions, 20 deletions

diff --git a/pyasn1/codec/ber/decoder.py b/pyasn1/codec/ber/decoder.py
index f2c4e4a..82bf19a 100644
--- a/pyasn1/codec/ber/decoder.py
+++ b/pyasn1/codec/ber/decoder.py
@@ -284,7 +284,7 @@ class NullDecoder(AbstractSimpleDecoder):
 
         head, tail = substrate[:length], substrate[length:]
 
-        component = self._createComponent(asn1Spec, tagSet, None, **options)
+        component = self._createComponent(asn1Spec, tagSet, noValue, **options)
 
         if head:
             raise error.PyAsn1Error('Unexpected %d-octet substrate for Null' % length)
diff --git a/pyasn1/type/base.py b/pyasn1/type/base.py
index 3270e0a..5d5d71b 100644
--- a/pyasn1/type/base.py
+++ b/pyasn1/type/base.py
@@ -119,7 +119,7 @@ class Asn1ItemBase(Asn1Item):
     @staticmethod
     def isNoValue(*values):
         for value in values:
-            if value is not None and value is not noValue:
+            if value is not noValue:
                 return False
         return True
 
@@ -185,8 +185,9 @@ class NoValue(object):
 
     def __getattr__(self, attr):
         if attr in self.skipMethods:
-            raise AttributeError('attribute %s not present' % attr)
-        raise error.PyAsn1Error('No value for "%s"' % attr)
+            raise AttributeError('Attribute %s not present' % attr)
+
+        raise error.PyAsn1Error('Attempted "%s" operation on ASN.1 schema object' % attr)
 
     def __repr__(self):
         return '%s()' % self.__class__.__name__
@@ -201,7 +202,7 @@ class AbstractSimpleAsn1Item(Asn1ItemBase):
 
     def __init__(self, value=noValue, **kwargs):
         Asn1ItemBase.__init__(self, **kwargs)
-        if value is noValue or value is None:
+        if value is noValue:
             value = self.defaultValue
         else:
             value = self.prettyIn(value)
@@ -307,7 +308,7 @@ class AbstractSimpleAsn1Item(Asn1ItemBase):
           :
               new instance of |ASN.1| type/value
         """
-        if value is noValue or value is None:
+        if value is noValue:
             if not kwargs:
                 return self
 
@@ -349,7 +350,7 @@ class AbstractSimpleAsn1Item(Asn1ItemBase):
          :
              new instance of |ASN.1| type/value
         """
-        if value is noValue or value is None:
+        if value is noValue:
             if not kwargs:
                 return self
 
@@ -448,7 +449,7 @@ class AbstractConstructedAsn1Item(Asn1ItemBase):
         representation = '%s(%s)' % (self.__class__.__name__, ', '.join(representation))
         if self._componentValues:
             for idx, component in enumerate(self._componentValues):
-                if component is None or component is noValue:
+                if component is noValue:
                     continue
                 representation += '.setComponentByPosition(%d, %s)' % (idx, repr(component))
         return representation
diff --git a/pyasn1/type/univ.py b/pyasn1/type/univ.py
index 8e78f77..f30e631 100644
--- a/pyasn1/type/univ.py
+++ b/pyasn1/type/univ.py
@@ -414,7 +414,7 @@ class BitString(base.AbstractSimpleAsn1Item):
             return self.bitLength
 
     def __init__(self, value=noValue, **kwargs):
-        if value is noValue or value is None:
+        if value is noValue:
             if kwargs:
                 try:
                     value = self.fromBinaryString(kwargs.pop('binValue'), internalFormat=True)
@@ -428,7 +428,7 @@ class BitString(base.AbstractSimpleAsn1Item):
                 except KeyError:
                     pass
 
-        if value is noValue or value is None:
+        if value is noValue:
             if self.defaultBinValue is not noValue:
                 value = self.fromBinaryString(self.defaultBinValue, internalFormat=True)
 
@@ -839,7 +839,7 @@ class OctetString(base.AbstractSimpleAsn1Item):
 
     def __init__(self, value=noValue, **kwargs):
         if kwargs:
-            if value is noValue or value is None:
+            if value is noValue:
                 try:
                     value = self.fromBinaryString(kwargs.pop('binValue'))
 
@@ -852,7 +852,7 @@ class OctetString(base.AbstractSimpleAsn1Item):
                 except KeyError:
                     pass
 
-        if value is noValue or value is None:
+        if value is noValue:
             if self.defaultBinValue is not noValue:
                 value = self.fromBinaryString(self.defaultBinValue)
 
@@ -1158,7 +1158,7 @@ class Null(OctetString):
     Parameters
     ----------
     value : :class:`str` or :py:class:`~pyasn1.type.univ.Null` object
-        Python empty string literal or *Null* class instance.
+        Python empty string literal or any object that evaluates to `False`
 
     tagSet: :py:class:`~pyasn1.type.tag.TagSet`
         Object representing non-default ASN.1 tag(s)
@@ -1168,7 +1168,6 @@ class Null(OctetString):
     : :py:class:`pyasn1.error.PyAsn1Error`
         On constraint violation or bad initializer.
     """
-    defaultValue = ''.encode()  # This is tightly constrained
 
     #: Set (on class, not on instance) or return a
     #: :py:class:`~pyasn1.type.tag.TagSet` object representing ASN.1 tag(s)
@@ -1232,6 +1231,11 @@ class Null(OctetString):
         """
         return OctetString.subtype(self, value, **kwargs)
 
+    def prettyIn(self, value):
+        if value:
+            return value
+
+        return octets.str2octs('')
 
 if sys.version_info[0] <= 2:
     intTypes = (int, long)
@@ -1879,9 +1883,6 @@ class SequenceOfAndSetOfBase(base.AbstractConstructedAsn1Item):
         IndexError:
             When idx > len(self)
         """
-        if value is None:  # backward compatibility
-            value = noValue
-
         componentType = self.componentType
 
         try:
@@ -2319,9 +2320,6 @@ class SequenceAndSetBase(base.AbstractConstructedAsn1Item):
         -------
         self
         """
-        if value is None:  # backward compatibility
-            value = noValue
-
         componentType = self.componentType
         componentTypeLen = self._componentTypeLen